The present invention relates to coated cemented carbide bodies particularly useful in tools for turning, milling and drilling of steels and stainless steels.
Cemented carbide bodies are manufactured according to powder metallurgical methods including milling, pressing and sintering. The milling operation is an intensive mechanical milling in mills of different sizes and with the aid of milling bodies. The milling time is of the order of several hours up to days. Such processing is believed to be necessary in order to obtain a uniform distribution of the binder phase in the milled mixture, but it results in a wide WC grain size distribution.
In U.S. Pat. Nos. 5,505,902 and 5,529,804 methods of making cemented carbide are disclosed according to which the milling is essentially excluded. Instead, in order to obtain a uniform distribution of the binder phase in the powder mixture, the hard constituent grains are precoated with the binder phase, the mixture is further wet mixed with pressing agent dried, pressed and sintered. In the first mentioned patent the coating is made by a SOL-GEL method and in the second, a polyol is used.
EP-A-665 308 discloses a coated cutting insert with a bimodal distribution of WC grain size with WC grains in two groups 0.1-1 μm and 3-10 μm. The insert according to this application is produced with conventional milling technique resulting in a broadening of the WC grain size distribution.